SNP Shot: Genomic Insights

GM1 gangliosidosis is a genetic disease that damages neurons in the brain and spinal cord. It's typically categorized into three main types, distinguished by the age of symptom onset. However, because the symptoms of these types can overlap, some researchers view GM1 gangliosidosis as existing on a spectrum rather than as distinct conditions.

Type I, also called the infantile form, is the most severe. Symptoms usually appear by 6 months of age. Infants initially develop normally, but then their development slows and their muscles become weak. They lose previously acquired skills (developmental regression) and may have an exaggerated startle response. Enlargement of the liver and spleen (hepatosplenomegaly) and skeletal abnormalities develop over time. Children with type I often experience seizures and severe intellectual disability.

Vision loss can occur in type I due to clouding of the cornea and damage to the retina. A characteristic "cherry-red spot" appears in the eye. Some individuals have distinctive "coarse" facial features, enlarged gums (gingival hypertrophy), and a weakened, enlarged heart muscle (cardiomyopathy). Individuals with type I usually do not live beyond early childhood.

GM1 gangliosidosis type II has two subtypes: late infantile and juvenile. Children with type II develop normally at first, with symptoms appearing around 18 months (late infantile) or 5 years (juvenile). These individuals experience developmental regression, but they typically do not develop cherry-red spots, coarse facial features, or enlarged organs. Type II progresses more slowly than type I but still reduces lifespan. People with the late infantile form typically survive until mid-childhood, while those with the juvenile form may live into early adulthood.

GM1 gangliosidosis type III, also known as the adult or chronic form, is the mildest. Symptom onset varies, but most affected individuals develop signs in their teens. Key features include involuntary muscle tensing (dystonia) and spinal bone abnormalities (vertebrae). Life expectancy varies among individuals with type III.

Inheritance:

GM1 gangliosidosis follows an autosomal recessive inheritance pattern. This means that an individual must inherit two copies of the mutated gene, one from each parent, to develop the condition. The parents, who each carry one copy of the altered gene, typically do not show any signs or symptoms of the disorder.